Determination of Freon-Insoluble Solids in Twenty Per Cent Pyrethrum Extracts HERMAN WACHS, CHARLES MORRIELLO, AND STEPHEN MAGES Research Department, Dodge and Olcott Co., Bayonne, N. 1.
A test tube is described which permits quick determinations of the solubility of pyrethrum extracts in Freon. This tube may b e used generally for solubility determinations under pressure in solvents which are gases under normal pressures.
Table 1. Freon-lnsolubles in 90% Pyrethrum Extract Sample InsolSample InsolNo. ubles Deviation No. ublea Deviation % % % % 1 2
HE bulk of the pyrethrum flowers now imported into this
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country is processed into extracts containing 20% pyrethrins. These extracts, after addition of sesame oil, are dissolved in Freon 12 and thus form the basis of the aerosol insecticide sprays (1). While the pyrethrins themselves are perfectly soluble in Freon, 20y0pyrethrum extracts will vary in solubility, depending on the degree to which natural impurities insoluble in Freon have been removed and on the care exercised to avoid formation of pyrethrin polymerization products. Such products when assayed for pyrethrin content by the A.O.A.C. or Sei1 method may show a pyrethrin content as high as 50'%, but when tested against insects, they are practically inactive. TheFe polymerization products are insoluble in Freon. An extract containing a large proportion of insolubles therefore has less active pyrethrins available than the assay indicates. This consideration and the obvious difficulties of handling a 20% Dvrethrum extract which contains a considerable portion of .in&luble solids make desirable a quick laboranna A tory method for determining the percentage of F reo n-i ns olu ble solids. This laboratory has worked out a test proced u r e w h i c h g i v e s sufficiently reproducible results t o serve as a basis for judging pyrethrum extracts. The equipment, shown in Figure 1, is simple and may be quickly assembled. A sample of 20% extract is weighed into a glass test tube, Freon is added the tube is centrifuged to coagulate suspended resins, the insolubles are filtered through a felt pad, the tube is washed several times with Freon, and the u n d i s s o l v e d portion is weighed. TEST ,If is a metal tube S c i e n t i f i c Glass Co. atalog No, 3810) designed to hold 5O-ml.-centrifuge t u b e s , Through M two slots, N , have been cut on opposite sides to make the contents of tube J visible. J is a Pyrex tube of 2-mm. wall thickness and an outside diameter of 29 mm. which fits into M without too much play. It is 92 mm. long and rests in the metal shield on t h e rubber
4 5
6 7 8 9 10
11 12 13 14
2.09 2.40 2.07 1.82
0.31
15
0.21
16
0.06
17
0.03
18
0.11
19
0.01
20
0.04
21
0.04
22
0.00
23
0.31
24
0.11 0.09
25
0.31
26
0.25
27
1.98 2.03 1.89 1.87 0.47 0.46 2.22 2.31 0.34 0.33 3.54 3.42 2.54 2.44 2.68 2.68 2.49 2.40 0.84 0.82 0.87 0.82 0.76 0.87 0.78 1.54 1.37 39.81 40.65
0.05 0.02 0.01 0.09
0.01 0.12
0.10 0.00 0.09 0.05
0.11 0.17 0.84
cushion, 0. H is a perforated metal screen which serves as a seat for a white felt pad, G, about 2 mm. thick and a piece of filter paper, F which is placed on top of the felt. H i s soldered to the metal dire stand, I . The felt and the filter aper are cut with a cork borer to fit tightly into J. E is a pergrated metal screen placed on the filter paper. The height of I is such that E is just below the top of J,when I rests on the bottom of the glass test tube. L is a brass flange with 4 threaded holes, held in place by the collar, K , of tube M . The top flange, B, is countersunk to hold a neoprene washer, C. A is an air valve of the type used on automobile tires, soldered into the center oi the top k n g e . OPERATING PROCEDURE. Approximately 1.8 cc. of the sample to be tested are weighed into the empty test tube J . The tube is placed in shell M and I is brought into the test tube, followed by the felt, the paper filter, finally plate E, and the top and bottom flanges are screwed together. Thirty grams of Freon are charged into the test tube out of a Freon cylinder which is turned upside down and has a pressure hose connected to the outlet. This hose is closed by a self-closing valve such as are used by gasoline stations for putting air in tires. By pressing valve A against the valve in the hose, Freon is released into the test tube. M may be marked to indicate the height of liquid corresponding to 30 grams of Freon. The test tube assembly is now placed in a beaker of water a t 25" C. and kept there for about 5 minutes, turned up and down a few times to ensure proper solution, then centrifuged for 5 minutes in a clinical type of centrifuge. Now the tube is turned upside down and the Freon solution discharged by slowly pressing on A . Thirty grams of Freon are charged into the tube again and the procedure is repeated: bringing to 25" C., centrifuging, and discharging. One or two additional washes with 20 rams of Freon may be required to make sure that all the solubfe material is removed. KO centrifuging is necessary for these washes. If the 6rst wash liquor is colorless, the second wash is not necessary. Additional washes do not affect the final result. After the last Freon wash has been discharged from the test tube, the tube is opened. Filter paper F is removed from the test tube, held with forceps, and any solid adhering t o it is washed with benzene with the aid of a capillary pipet with rubber bulb into a tared crystallizing dish 75 mm. in diameter. This filter paper will usually be found to be clean. The felt is now removed from the test tube, held with the forceps, and washed with ben-
TUB^.
Figure 1.
5.61 5.30 3.25 3.46 4.44 4.38 3.50 3.47 4.14 4.03 3.09 3.08 2.20 2.16 1.05 1.09 3.18 3.18 3.38 3.07 1.21 1.33 1.96 2.05
Equipment
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INDUSTRIAL AND ENGINEERING CHEMISTRY
454
The benzene solution is evaporated”oh a steam bath, the residue is placed for 20 minutes in a drying oven a t about 90” to 100” C., and the dish is weighed: Weight of residue X 100 = Weight of sample
5 Freon-insoluble solids
The ability to reprodbce resu!ts is shown in Table I. The standard error of the mean of two duplicates of the first 26 samples
Vol. 16, No. 7
ment. While this procedure was worked out for determining the solubility- of _wrethrum extracts in Freon. it can be used for solubility _ determinations of other substances ‘in solvents which are gases under normal pressures. LITERATURE CITED
(1) Goodhue, L. D.,IND.ENO.CHEM.,34,1456 (1942).
Simple Cpnstant Reflux Take-Off for Distillation Systems J O H N C. SNYDER
AND
WALTER STEUBER, Catrlytic Development Corporation, Marcus Hook, Pa.
IN
LABORATORY fractional distillation it is often necessary to control the reflux ratio so that it is kept constant, regardless of variations in the distillation rate or empirical factors. This has been accomplished by Carter and Johnson (9) with a magnetically moved funnel, by Bruun ( 2 ) with a two-way valve and capillaries, and by Podbielniak (3) with an automatic valve seated in the take-off tube. All these devices require a degree of skill too great for fabrication by an amateur glass blower, and various mechanical difficulties have been experienced in their operation, due to sticking of moving parts or plugging of capillaries. An easily constructed take-off device of the intermittent type which operates smoothly is described in this paper.
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STILL CONSTRUCTION AND O P E R A T l O N
The takeoff is designed for use with any type of total condensing head in which the entire condensate stream passes a point on its return to the column (see Figure 1). The rec,eiver is maintained under a sli h t pressure sufficient to prevent the flow of liquid from the s t i i head through the U-shaped tube into the r e ceiver. A small steady stream of inert gas passing through the nonvolatile oil in the bubbler supplies this pressure. Periodically, the receiver is vented to the operating pressure of the still through an electrically o erated valve controlled by a cycle timer. During this period t\e entire condensate flows by gravity to the receiver, by the merhanism shown in Figure 2. While the receiver is under pressure,,the liquid in the takeoff ca illary is maintained at levels A , A When the pressure is r e L e d , the liquid flows to levels B, B’, which are just at the overflow point. Consequently, all reflux during the “on” period enters the take-off at A and an equal amount of liquid overflows a t B’ into the receiver. At the end of the “on” interval (generally from 2 to 5 seconds), the valve closes and restoration of the receiver to pressure quickly interrupts the take-off stream. For
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TO ADPlTlONAL STILLS
! j
TO ATMOSPHERE OR VACUUM PUMP
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RECEIVER
Figure 2.
Detail of Take-Off Line
convenience in emptying the receiver, the take-off line is generally rovided with a stopcock to revent the flow during this per,iod. kowever, if it is desired to [eep the roduct from coming into contact with stopcock grease, and if low-boiling components which will vaporize in the take-off line at the outset of the dmtillation are absent, this stopcock and the one on the receiver may be omitted. The dimensions of the takeoff line de end maiply upon the throu hput of the still, but are not critica?. The diameter must be suhcient to accommodate the entire dist!late during the t a k e off period. A convenient length for Ah, which indicates the pressure head that is maintained by the bubbler, is from 0.5 to 3 cm. The following advantages have been noted:
r
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PRESSURE coma
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Simplicity of construction, operation, and adjustment. The take-off maintains a constant reflux ratio, irrespective of distillation rate, which is redetermined by simple adjustment of the intervals of an on-ancfoff timer. Low cost. No delicate moving parts in the still head. Very low holdup. Distillations may be conducted out of contact with anything save glass and an inert gas. The method is adaptable, LO distillation at other than atmospheric pressure. Several stills may be operated with the same control system.
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LITERATURE CITED
i
Figure 1. Flow Diagram
(1) Bruun, J. H.,IND. ENO.CHWM., ANAL.ED.,7, 359 (1935). (2) Carter, A. S., and Johnson, F.W. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,251,185 (July 29, 1941). (3) Podbieiniak, W. J., Podbielniak Centrifugal Super-contactor Co.,Circular 22 (Nov , 1942).
